ERC-4337 AA33 Reverted: Paymaster Validation Failure Fix

To resolve ERC-4337 AA33 Reverted: Paymaster Validation Failure Fix, fix ERC-4337 EntryPoint AA33 reverted errors. Debug validatePaymasterUserOp verification reverts, token allowance deficits, and gas limit underestimations. Ensure all derivation paths, environment parameters, and cryptographic signatures are verified client-side using deterministic tools before broadcasting live transactions.

The ERC-4337 EntryPoint error AA33 reverted (or empty return data) occurs strictly during the pre-execution validation phase when the paymaster’s validatePaymasterUserOp reverts. Common causes include expired paymaster signatures, insufficient ERC-20 token allowances, or an underestimated paymasterVerificationGasLimit under EntryPoint v0.7. Because AA33 triggers before account execution, UserOperation calldata never executes and no state changes occur.

To inspect the packed paymasterAndData hex payload and simulation parameters offline, paste your UserOperation into our interactive ERC-4337 Calldata Decoder Tool. For general bundler simulation drops, consult our guide on ERC-4337 UserOperation reverts and paymaster errors.

Architectural Breakdown: Lifecycle of a UserOperation

To isolate why AA33 occurs, consider the three distinct execution stages orchestrated by EntryPoint.handleOps:

   ┌─────────────────────────────────────────────────────────────┐
   │ 1. VALIDATION PHASE (Pre-Execution Verification)           │
   │    a) Sender Account: validateUserOp()                     │
   │    b) Paymaster: validatePaymasterUserOp()  ───► Revert?   │
   │                                              └──► EMITS AA33
   └──────────────────────────────┬──────────────────────────────┘
                                  │ (Validation Passes)
                                  ▼
   ┌─────────────────────────────────────────────────────────────┐
   │ 2. EXECUTION PHASE (Main User Call)                         │
   │    Sender Account: execute(userOp.callData)                 │
   └──────────────────────────────┬──────────────────────────────┘
                                  │
                                  ▼
   ┌─────────────────────────────────────────────────────────────┐
   │ 3. POST-EXECUTION PHASE (Optional Paymaster Settlement)     │
   │    Paymaster: postOp(mode, context, actualGasCost, ...)     │
   │                                             ───► Revert?   │
   │                                              └──► EMITS AA50
   └─────────────────────────────────────────────────────────────┘

Verified Implementation in Pinned EntryPoint Versions

The EntryPoint code demonstrates exactly where AA33 originates:

EntryPoint v0.6.0 (@account-abstraction/contracts@0.6.0, commit c8913c3)

In EntryPoint v0.6.0, _validatePaymasterUserOp handles paymaster verification:

// EntryPoint.sol (v0.6.0)
try IPaymaster(paymaster).validatePaymasterUserOp{gas: paymasterVerificationGasLimit}(userOp, userOpHash, maxCost) 
    returns (bytes memory _context, uint256 _validationData) {
    context = _context;
    validationData = _validationData;
} catch Error(string memory revertReason) {
    revert FailedOp(opIndex, string.concat("AA33 reverted: ", revertReason));
} catch {
    revert FailedOp(opIndex, "AA33 reverted");
}

If the paymaster reverts during validation, AA33 reverted is thrown. Conversely, if postOp fails in v0.6.0, it throws AA50 postOp revert, not AA33.

EntryPoint v0.7.0 (@account-abstraction/contracts@0.7.0, commit e1f8164)

In EntryPoint v0.7.0, the validation mechanism remains strictly separated:

// EntryPoint.sol (v0.7.0)
try IPaymaster(paymaster).validatePaymasterUserOp{gas: paymasterVerificationGasLimit}(userOp, userOpHash, maxCost) 
    returns (bytes memory _context, uint256 _validationData) {
    context = _context;
    validationData = _validationData;
} catch {
    revert FailedOp(opIndex, "AA33 reverted");
}

In v0.7.0, when postOp reverts after a successful user execution (PostOpMode.opSucceeded), EntryPoint does not immediately fail the transaction: it rolls back the inner call and re-invokes postOp with PostOpMode.postOpReverted. If that second call also fails, it reverts with AA50 postOp reverted.

The Primary Causes of AA33 Reverts

Because AA33 is caused by validatePaymasterUserOp throwing an exception, you must examine the specific checks performed inside that function:

1. Token Paymaster: Insufficient Balance or Allowance at Validation Time

For ERC-20 token paymasters (where the user pays gas in tokens such as USDC), validatePaymasterUserOp must guarantee that the user can cover the worst-case gas cost (maxCost = maxFeePerGas * (verificationGasLimit + callGasLimit + preVerificationGas)):

// Inside TokenPaymaster.sol (Validation Phase)
function validatePaymasterUserOp(UserOperation calldata userOp, bytes32 userOpHash, uint256 maxCost) 
    external returns (bytes memory context, uint256 validationData) {
    uint256 tokenMaxCost = getTokenEquivalent(maxCost);
    
    // FAILS HERE IF BALANCE OR ALLOWANCE IS INSUFFICIENT:
    require(IERC20(token).balanceOf(userOp.sender) >= tokenMaxCost, "Token balance too low");
    require(IERC20(token).allowance(userOp.sender, address(this)) >= tokenMaxCost, "Token allowance too low");
    
    return (abi.encode(userOp.sender, tokenMaxCost), 0);
}

If the smart account has an existing balance or allowance that is even slightly below tokenMaxCost, the require statement triggers an EVM revert, causing the EntryPoint to emit AA33 reverted.

2. Verifying Paymaster: Signature Verification Mismatch

In verifying paymasters (sponsoring gas via an off-chain API signature, e.g. Pimlico, Biconomy, Alchemy):

• Signer Key Mismatch: The hash signed by the off-chain paymaster service does not match the actual userOpHash or includes mismatched chain IDs.
• Malformed PaymasterAndData: The paymaster data passed in the UserOp does not match the expected ABI encoding of the paymaster contract.
• Expired Timestamp: While expired timestamps typically return an encoded validationData failure (AA32 paymaster expired), contracts that enforce timestamps via explicit require(block.timestamp <= validUntil) will throw an EVM revert, resulting in AA33.

3. Gas Exhaustion (paymasterVerificationGasLimit)

If paymasterVerificationGasLimit is estimated too aggressively, the paymaster’s validation logic runs out of gas during cryptographic hashing or oracle price lookups. Because the EntryPoint executes validatePaymasterUserOp with a bounded gas sub-call, an out-of-gas error inside the paymaster contract is caught by the catch block and returned as AA33 reverted.

Diagnostic Checklist & Verification

When troubleshooting AA33 in development or test environments, execute the following diagnostic checks:

Step 1: Inspect EntryPoint Simulation Traces

Run your simulation using debug RPC calls (debug_traceCall with JavaScript tracer or Foundry fork simulation):

cast rpc eth_estimateUserOperationGas '<userOpJson>' '0x0000000071727De22E5E9d8BAf0edAc6f37da032'

Inspect the internal call trace: verify whether the call from EntryPoint to IPaymaster(paymaster).validatePaymasterUserOp returns a custom revert string or executes an REVERT opcode.

Step 2: Verify Token Allowance and Balance Margins

If using an ERC-20 paymaster, ensure that before building the UserOperation, the account’s token balance and allowance to the paymaster satisfy: $$\text{Current Allowance} \ge \text{maxCost} \times \text{PriceRatio} \times \text{SafetyBuffer}$$

// Sample verification check (pre-flight validation)
async function verifyPaymasterEligibility(
  client: any,
  tokenAddress: `0x${string}`,
  accountAddress: `0x${string}`,
  paymasterAddress: `0x${string}`,
  maxCostInTokens: bigint
) {
  const [balance, allowance] = await Promise.all([
    client.readContract({ address: tokenAddress, abi: erc20Abi, functionName: 'balanceOf', args: [accountAddress] }),
    client.readContract({ address: tokenAddress, abi: erc20Abi, functionName: 'allowance', args: [accountAddress, paymasterAddress] })
  ]);

  if (balance < maxCostInTokens) {
    throw new Error(`AA33 Hazard: Token balance (${balance}) < required maxCost (${maxCostInTokens})`);
  }
  if (allowance < maxCostInTokens) {
    throw new Error(`AA33 Hazard: Token allowance (${allowance}) < required maxCost (${maxCostInTokens})`);
  }
  return true;
}

Step 3: Check Paymaster Verification Gas Allocations

• In EntryPoint v0.6: Increase verificationGasLimit to provide sufficient headroom for paymaster signature verification.
• In EntryPoint v0.7: Ensure paymasterVerificationGasLimit is explicitly set and accounts for contract state reads, oracle queries, and ECDSA/P-256 signature recovery.

Primary Technical References & Specifications

• ERC-4337 EntryPoint Specification: EIP-4337: Account Abstraction Using Alt Mempool
• Canonical EntryPoint v0.6.0 Source: eth-infinitism/account-abstraction (v0.6.0 / commit c8913c3)
• Canonical EntryPoint v0.7.0 Source: eth-infinitism/account-abstraction (v0.7.0 / commit e1f8164)
• Companion Diagnostic: ERC-4337 UserOperation Reverts at Paymaster: PostOp & Validation Failures

ERC-4337 EntryPoint Error Code Reference Matrix

Cross-reference standard ERC-4337 EntryPoint revert codes across account abstraction and smart wallet layers:

[!TIP] Unpack packed UserOperations, calculate prefund requirements, and isolate simulation hazards in our air-gapped /tools/erc4337-calldata-decoder/.